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Nanostructured films consisting of single Si nanoparticles (NPs) and Er3+ ions layers separated by nanometer-scale Al2O3 layers of controlled thickness have been prepared in order to tune the energy transfer between Si NPs and Er3+ ions. The amorphous Si NPs with an effective diameter of ∼4.5 nm are formed during growth and are able to sensitize the Er3+ ions efficiently with no postannealing treatments. The characteristic distance for energy transfer from Si NPs to Er3+ ions in Al2O3 is found to be in the 1 nm range. It is shown that in the nanostructured films, it is possible to achieve an optimized configuration in which almost all the Er3+ ions have the potential to be excited by the Si NPs. This result stresses the importance of controlling the dopant distribution at the nanoscale to achieve improved device performance. [ABSTRACT FROM AUTHOR]

Weshow that dye-doped polymers open an interesting route to controllinglight at the nanoscale. Just as for the much better known metal-basedplasmonic systems, propagating and localized modes are possible. Weshow that the attractive features offered by plasmonics, specificallyenhanced optical fields and subwavelength field confinement, are alsoavailable with these materials. They thus open a new opportunity innanophotonics in which fabrication and functionality might be achievedby harnessing molecular and supramolecular chemistry. [ABSTRACT FROM AUTHOR]

Abstract: Nanostructured Er3+–Si nanoparticles (NPs) codoped Al2O3 films were synthesized by a one step laser based deposition process which allows to form the Si NPs in situ at room temperature, and to control their size and separation with the Er ions in the nanoscale. Two different thermal annealing treatments are studied in order to optimize the photoluminescence (PL) emission: rapid thermal annealing (RTA) at 900°C during 2min, and conventional furnace step annealing at different temperatures up to 750°C for 1h. After RTA process the films show an important enhancement on the photoluminescence lifetime values which is related to a reduction of the non-radiative decay channels. Nevertheless, the Si NPs to Er ions energy transfer is strongly reduced. In contrast after conventional furnace annealing up to 700°C, although there is only a moderate increase of the photoluminescence lifetime values, the excitation of Er ions through Si NPs is still active and as a consequence a large enhancement of the photoluminescence intensity with respect to the Er-only doped film is achieved. These different behaviours are most likely related to structural and chemical changes in the Er environment upon the different annealing processes. [Copyright &y& Elsevier]

Abstract: Enhancement of the 1540nm emission in nanostructured Er3+-doped a-Si/a-Al2O3 thin films prepared by pulsed laser deposition is studied. This paper is focused on a symmetric film structure formed by a central Er3+-doped Al2O3 layer sandwiched between two a-Si layers, which are isolated from the silicon substrate and the ambient medium by non-doped Al2O3 buffer layers. The layer thicknesses have been chosen in order to minimize the reflectance of the film at the pumping wavelength of 514.5nm and thus to increase the effective excitation of the Er3+ ions. The Er3+ ions within the central Er3+-doped Al2O3 layer have been distributed in layers separated by about 5nm in order to minimize clustering and concentration quenching effects. Upon excitation at 514.5nm, the film annealed at 700°C shows the characteristic emission of Er3+ ions at 1540nm in addition to a continuous emission band, which is also observed upon excitation at 476nm while no Er3+ related emission can be evidenced. This band may thus be linked to emission from the Si layers. It has been determined that the net Er3+ emission intensity enhancement at 1540nm is of a factor 1.5 when compared to a film prepared with no Si layers. A two-component luminescence decay is observed upon excitation at 514.5nm: first, a fast decay regime that can be associated to the broad emission band from the Si layers, and then a slower decay regime linked to the Er3+ emission and characterized by a time constant of 5.7ms. This lifetime value is 2.5 times higher than for the film without silicon layers (2.2ms). [Copyright &y& Elsevier]

Abstract: The formation and optical response of VO x nanoparticles embedded in amorphous aluminium oxide (Al2O3) thin films by pulsed laser deposition is studied. The thin films have been grown by alternate laser ablation of V and Al2O3 targets, which has resulted in a multilayer structure with embedded nanoparticles. The V content has been varied by changing the number of pulses on the V target. It is found that VO x nanoparticles with dimensions around 5nm have been formed. The structural analysis shows that the vanadium nanoparticles are oxidized, although probably there is not a unique oxide phase for each sample. The films show a different optical response depending on their vanadium content. Optical switching as a function of temperature has been observed for the two films with the highest vanadium content, at transition temperatures of about −20°C and 315°C thus suggesting the presence of nanoparticles with compositions V4O7 and V2O5, respectively. [Copyright &y& Elsevier]

The efficient excitation of Er3+ ions through contact with Si nanoparticles (NPs) is demonstrated. A nanostructured doping process has been developed that leads to contact between Si NPs formed in situ and optically-active Er3+ ions embedded in Al2O3. This is achieved by independent and consecutive deposition of the dopants and matrix. The Si NP-Er3+ contact regime enhances the probability of efficient interaction due to the local spatial overlap of the electronic states of the Er3+ and of the Si NP exciton, enabling energy transfer by interband exciton recombination. This leads to up to 53% of the Er3+ ions being excited in as-deposited films. [ABSTRACT FROM AUTHOR]

A structured film formed by an active Er3+-doped amorphous Al2O3 layer located between two amorphous silicon nanolayers (NLs) in as-grown conditions shows an enhancement of the photoluminescence (PL) intensity and lifetime at 1.53 μm of one order of magnitude when compared to a similar Er3+-doped film without silicon NLs. The film can be pumped even under nonresonant excitation conditions as a result of a long range energy transfer from the a-Si NLs to the Er3+ ions. In addition, the PL shows a single exponential decay with a lifetime value as high as 2.4 ms. The lifetime enhancement is associated with an improvement of the emission efficiency of the Er3+ ions. [ABSTRACT FROM AUTHOR]

Noble metal nanoparticles, particularly gold and silver nanoparticles, have garnered significant attention due to their ability to manipulate light at the nanoscale through their localized surface plasmon resonance (LSPR). While their LSPRs below 1100 nm were extensively exploited in a wide range of applications, their potential in the near-infrared (NIR) region, crucial for optical communication and sensing, remains relatively underexplored. One primary reason is likely the limited strategies available to obtain highly stable plasmonic nanoparticles with tailored optical properties in the NIR region. Herein, we synthesized AuAg nanorattles (NRTs) with tailored and narrow plasmonic responses ranging from 1000 to 3000 nm. Additionally, we performed comprehensive characterization, employing advanced electron microscopy and various spectroscopic techniques, coupled with finite difference time domain (FDTD) simulations, to elucidate their optical properties. Notably, we unveiled the main external and internal LSPR modes by combining electron energy-loss spectroscopy (EELS) with surface-enhanced Raman scattering (SERS). Furthermore, we demonstrated through surface-enhanced infrared absorption spectroscopy (SEIRA) that the NRTs can significantly enhance the infrared signals of a model molecule. This study not only reports the synthesis of plasmonic NRTs with tunable LSPRs over the entire NIR range but also demonstrates their potential for NIR sensing and optical communication., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Plexcitonic nanoparticles exhibit strong light-matter interactions, mediated by localized surface plasmon resonances, and thereby promise potential applications in fields such as photonics, solar cells, and sensing, among others. Herein, these light-matter interactions are investigated by UV-visible and surface-enhanced Raman scattering (SERS) spectroscopies, supported by finite-difference time-domain (FDTD) calculations. Our results reveal the importance of combining plasmonic nanomaterials and J-aggregates with near-zero-refractive index. As plexcitonic nanostructures nanorattles are employed, based on J-aggregates of the cyanine dye 5,5,6,6-tetrachloro-1,1-diethyl-3,3-bis(4-sulfobutyl)benzimidazolocarbocyanine (TDBC) and plasmonic silver-coated gold nanorods, confined within mesoporous silica shells, which facilitate the adsorption of the J-aggregates onto the metallic nanorod surface, while providing high colloidal stability. Electromagnetic simulations show that the electromagnetic field is strongly confined inside the J-aggregate layer, at wavelengths near the upper plexcitonic mode, but it is damped toward the J-aggregate/water interface at the lower plexcitonic mode. This behavior is ascribed to the sharp variation of dielectric properties of the J-aggregate shell close to the plasmon resonance, which leads to a high opposite refractive index contrast between water and the TDBC shell, at the upper and the lower plexcitonic modes. This behavior is responsible for the high SERS efficiency of the plexcitonic nanorattles under both 633 nm and 532 nm laser illumination. SERS analysis showed a detection sensitivity down to the single-nanoparticle level and, therefore, an exceptionally high average SERS intensity per particle. These findings may open new opportunities for ultrasensitive biosensing and bioimaging, as superbright and highly stable optical labels based on the strong coupling effect., (© 2023 The Authors. Small published by Wiley‐VCH GmbH.)

This review provides an overview of current progress in Pd nanoparticles supporting localized surface plasmon resonance and their applications. We begin by analyzing briefly the optical properties of Pd putting particular focus on outlining the origin of its size- and shape-dependent LSPR, high refractive index sensitivity, and high absorption contribution. The differences in the optical behavior with Au and Ag, the primary plasmonic materials, are highlighted. The main strategies to synthesize Pd nanoparticles, pure or hybrid, with well-defined optical properties are then reviewed. In this section, we include only those works that carry out the study of the optical properties of the nanoparticles. The applications of plasmonic Pd nanoparticles are also discussed in detail. This review is concluded with a section devoted to the future perspectives highlighting the most relevant challenges to be addressed to take Pd nanoparticles from the laboratory to real applications.

Raman-encoded gold nanoparticles (NPs) have been widely employed as photostable multifunctional probes for sensing, bioimaging, multiplex diagnostics, and surface-enhanced Raman scattering (SERS)-guided tumor therapy. We report a strategy toward obtaining a particularly large library of Au nanocapsules encoded with Raman codes defined by the combination of different thiol-free Raman reporters, encapsulated at defined molar ratios. The fabrication of SERS tags with tailored size and predefined codes is based on the in situ incorporation of Raman reporter molecules inside Au nanocapsules during their formation via galvanic replacement coupled to seeded growth on Ag NPs. The hole-free closed-shell structure of the nanocapsules is confirmed by electron tomography. The unusually wide encoding possibilities of the obtained SERS tags are investigated by means of either wavenumber-based encoding or Raman frequency combined with signal intensity, leading to an outstanding performance as exemplified by 26 and 54 different codes, respectively. We additionally demonstrate that encoded nanocapsules can be readily bioconjugated with antibodies for applications such as SERS-based targeted cell imaging and phenotyping.

For decades, plasmonic nanoparticles have been extensively studied due to their extraordinary properties, related to localized surface plasmon resonances. A milestone in the field has been the development of the so-called seed-mediated growth method, a synthetic route that provided access to an extraordinary diversity of metal nanoparticles with tailored size, geometry and composition. Such a morphological control came along with an exquisite definition of the optical response of plasmonic nanoparticles, thereby increasing their prospects for implementation in various fields. The susceptibility of surface plasmons to respond to small changes in the surrounding medium or to perturb (enhance/quench) optical processes in nearby molecules, has been exploited for a wide range of applications, from biomedicine to energy harvesting. However, the possibilities offered by plasmonic nanoparticles can be expanded even further by their careful assembly into either disordered or ordered structures, in 2D and 3D. The assembly of plasmonic nanoparticles gives rise to coupling/hybridization effects, which are strongly dependent on interparticle spacing and orientation, generating extremely high electric fields (hot spots), confined at interparticle gaps. Thus, the use of plasmonic nanoparticle assemblies as optical sensors have led to improving the limits of detection for a wide variety of (bio)molecules and ions. Importantly, in the case of highly ordered plasmonic arrays, other novel and unique optical effects can be generated. Indeed, new functional materials have been developed via the assembly of nanoparticles into highly ordered architectures, ranging from thin films (2D) to colloidal crystals or supercrystals (3D). The progress in the design and fabrication of 3D supercrystals could pave the way toward next generation plasmonic sensors, photocatalysts, optomagnetic components, metamaterials, etc. In this Account, we summarize selected recent advancements in the field of highly ordered 3D plasmonic superlattices. We first analyze their fascinating optical properties for various systems with increasing degrees of complexity, from an individual metal nanoparticle through particle clusters with low coordination numbers to disordered self-assembled structures and finally to supercrystals. We then describe recent progress in the fabrication of 3D plasmonic supercrystals, focusing on specific strategies but without delving into the forces governing the self-assembly process. In the last section, we provide an overview of the potential applications of plasmonic supercrystals, with a particular emphasis on those related to surface-enhanced Raman scattering (SERS) sensing, followed by a brief highlight of the main conclusions and remaining challenges.